1. Field of the Invention
The present general inventive concept relates to an ink set including an ink composition including an encapsulated black pigment in which a black pigment is coated with a polymer resin and an ink composition including an encapsulated color pigment in which a color pigment is coated with a polymer resin, an ink cartridge including the ink set, and an inkjet recording apparatus including the ink cartridge, and more particularly, to an ink set that includes an ink composition including an encapsulated black pigment in which a black pigment is coated with a polymer resin and an ink composition including an encapsulated color pigment in which a color pigment is coated with a polymer resin, which is used to obtain high-quality images without nozzle clogging in an inkjet printing head, and in which a volume average diameter and glass transition temperature of the encapsulated black and color pigments are controlled.
2. Description of the Related Art
Inkjet ink includes a dye or a pigment. Dye is used to obtain high-quality color images but the obtained images cannot be preserved for a long time due to poor resistance of the dye to water and light. The pigment has good resistance to the water and the light but a resistance thereof to abrasion is low. In addition, the pigment has a narrow color gamut and a low optical density (OD) due to a shielding effect, and thus images obtained using pigment alone have a low-image quality. These problems can be resolved by using an encapsulating method in which particles of pigment are covered with a non-aqueous polymer. Encapsulated dye has a better durability, and encapsulated pigment has a wider color gamut. In addition, printed images obtained using the encapsulated pigment have a high resistance to abrasion and high image quality.
Meanwhile, presently, inkjet printers are widely available in homes and offices and have been developed such that inkjet printed images have as high quality as images obtained by silver-salt photography. An ink composition used in inkjet printers may have various properties according to an application thereof.
Text printing requires a high degree of visuality and a high OD. Accordingly, when printing text, a content of ejected ink should be high, and particles of a pigment should be large because, in general, OD is increased as the particle size of the pigment is increased. In addition, a polymer resin coated on the pigment should have a high glass transition temperature (Tg) because ink bleeding should be maintained at low levels on printing media.
Photo or picture color printing requires small nozzles to embody high-resolution images. Therefore, the pigment should be small. However, since conventional pigment is too small, the conventional pigment easily permeates into printing media and the OD of the printed images is decreased. Alternatively, as for encapsulated pigment ink, a polymer coated on a pigment acts as an adhesive between the encapsulated pigment ink and printing media and problems caused by the permeation of the pigment into printing media can be partially prevented. However, encapsulated pigment ink is less permeable with respect to printing media and thus, a cellulose of a portion of a sheet that does not contact the encapsulated pigment ink is directly exposed and a white hole effect occurs, thereby decreasing the image quality of the printed image.
When the pigment is coated with a polymer having a low glass transition temperature (Tg), particles of the pigment run on a printing medium and thus, direct exposure of a fabric of the printing medium can be prevented and high-quality color images can be obtained.
Meanwhile, in conventional inkjet printing heads, the size of black nozzles is equal to a size of color nozzles. However, in recently developed inkjet printing heads, the size of black nozzles is larger than the size of color nozzles to obtain both clear text and clear color images. However, conventional encapsulated color ink includes black and color ink of the same particle size and the same Tg, and thus when ejected through a smaller nozzle for color ink, a nozzle clogging phenomenon occurs. In addition, optimal images cannot be obtained according to applications.
Therefore, there is a need to develop an ink set to provide high-quality images by controlling a particle size of a capsulated pigment and Tg of respective ink compositions according to a printing purpose.